“Polymer particles” means particles composed of a resin, and the particles generally have a wide range of diameters from several tens of nm to several hundreds of μm. Different from polymer molded products such as films, fibers, injection molded products, and extrusion molded products, polymer particles are used for modification and improvement of various materials by utilizing the large specific surface area and the structure of microparticles.
Their major uses include modifiers for cosmetics, additives for toners, rheology modifiers for paints and the like, agents for medical diagnosis and examination, and additives for molded products such as automobile materials and construction materials. In particular, in recent years, they have been in wider use due to the advantageous microparticle structure of polymer particles, as materials for rapid prototyping and rapid manufacturing, which are techniques to produce custom-made molded products combining with laser processing technologies.
Recently, in fields of electronic information materials and the like such as liquid crystal displays or in fields of cosmetics and paints, for such polymer microparticles, there are increasing demands to be given with higher function and higher accuracy such as higher heat resistance, higher solvent resistance and higher uniformity in particle diameter distribution as compared with conventional ones.
Although among the polymer microparticles polyamide particles have been used since old times in the fields of cosmetic's and paints on account of the features of the raw material such as a strength or an appropriate moisture absorption, the trend in selecting the raw material from non-petroleum materials originating from biomass has been accelerated from the viewpoint of recent global environmental protection and, in particular, polyamide 1010 polymer particles are paid attention to from the viewpoints of functional features of the material and easiness of obtaining the raw material.
As the method of producing polyamide 1010 polymer particles, generally a method of mechanically grinding pellets of polyamide 1010 resin is employed. However, there are problems in points that the particles obtained by grinding are low in sphericity and that the particle diameter distribution is broad.
As a method of improving those efforts, although JP-A-2007-277546 proposes a method of producing polyamide polymer particles by melt-blending polyamide resin and a water soluble component and removing the water soluble component by water after the blending, it remains a problem on particle flowability though spherical particles are obtained.
Further, as represented by JP-A-2010-163618, although a method of dissolving polyamide resin into a solvent such as an alcohol by heating it in the solvent and precipitating polyamide polymer particles while lowering the temperature of the solvent is proposed, it is disclosed that the obtained particles are porous, and it is the present status that a further improved technology as functional microparticles is being required with respect to a point of particle flowability and the like (JP-A-2010-163618, JP-A-2011-218330 and JP-A-2011-219756).
On the other hand, as a method of forming polymer microparticles, although WO 2009/142231 has already proposed a method of obtaining polymer particles by dissolving two or more kinds of resins and utilizing an emulsion due to phase-separation phenomenon of polymer solution, a technical improvement has been required with respect to making polyamide resin, which is a crystalline polymer, into a form of particles.
In conventional methods of producing polyamide 1010 polymer particles, there are problems in flowability and slipperiness of polyamide 1010 polymer particles and, further, in the method wherein the particles become porous, there is a problem in mechanical strength in addition to particle flowability, and therefore, there is a problem in such a point that particle breakage occurs.
It could therefore be helpful to provide polyamide 1010 polymer particles formed in a shape high in sphericity and crystallinity and excellent in particle flowability and mechanical properties such as stiffness.